Hall effect sensors are based on the Hall effect, which was named after its discoverer Edwin Hall in 1879. Typically, a constant current is provided to a Hall element or plate and a magnetic field is applied perpendicular to the current flowing through the Hall plate. Charge carriers in the Hall plate are deflected due to the Lorentz force to create a Hall voltage that is perpendicular to both the magnetic field and the current flow. This Hall voltage can be measured and is directly proportional to the magnetic field. Hall effect sensors are used for speed, rotational speed, linear position, linear angle and position measurements in automotive, industrial and consumer applications. Usually, Hall sensor integrated circuit chips include one or more Hall plates and signal conditioning circuitry, such as an amplifier.
Typically, a differential Hall effect sensor includes two Hall plates and a differential amplifier. The Hall plates are coupled to the differential amplifier and provide Hall voltages to the differential amplifier, such that the difference between magnetic field fluxes at the Hall plates is detected and amplified to provide an output signal. Differential Hall effect sensors can be used to detect the motion and position of ferromagnetic and permanent magnet structures. To detect ferromagnetic objects, such as a toothed ferromagnetic wheel, the magnetic field is provided via a back biasing permanent magnet.
Testing a differential Hall effect sensor includes applying a differential magnetic field to the sensor, such that the two Hall plates receive different or in best case opposing magnetic field fluxes. However, it's difficult to generate a differential magnetic field over small Hall plate distances at the surface of a sensor via a coil and magnetic core system. Mechanical positioning tolerances between the sensor and the magnetic core are tight and inaccurately positioning the sensor in the differential magnetic field leads to measurement errors that reduce product yields. Close contact between a sensor and the magnetic core produces large differential magnetic fields at the surface of the sensor and keeps mechanical positioning errors small. However, close contact between the sensor and the magnetic core leads to abrasion of the magnetic core over time and unstable measurements. Also, inaccurately positioning a sensor in a package contributes to measurement errors.
For these and other reasons there is a need for the present invention.